Current multi-chip circuitry design requires the attachment of numerous integrated circuit chips to high density multi-layer interconnect (HDMI) substrates (or boards) for multi-chip-modules (MCM). The electrical interconnects normally include surface pads for bonding to surface mounted chips, a dielectric, and electrical lines buried in the dielectric for connecting selected pads to provide electrical routing between various bond sites on the chips. It is common to use copper for the buried lines and polyimide as the dielectric. The copper lines may form separate layers of orthogonal wiring sets that are interconnected to the surface pads by vertical metal pillars.
Obviously cost is an important factor in any substrate fabrication approach. The cost tends to be closely associated with the number of fabrication steps. Normally, additional steps not only increase the labor and material costs as well as the process complexity, but also decrease yields. Thus a mature substrate fabrication process which reduces the number of fabrication steps to produce an equivalent structure will typically reduce costs and improve yields.